Railway car retarder control system



H. c. KENDALL ETAL 3,125,315

RAILWAY RETARDER CONTROL SYSTEM 7 Sheets-Sheet 1 March 17, 1964 Filed June 2, 1953 March 17, 1964 Filed June 2, 1955 FREAMPLIFIERv I3 H. C. KENDALL ETAL RAILWAY CAR RETARDER CONTROL SYSTEM vvvvv AMIXER I2 CRYSTAL RECTIFIER TRANSMITTING H OR N CAVITY RESONATOR 24 AND RECEIVING /IO CONTINUOUS wAvE UHF oscILLAToR II AMPLIFIER AND PULSE FORMER I4 7 Sheets-Sheet 2 INVENToRS HGKENDALL K AND JI-IAUER JR.

THEIR ATTORNEY March 17, 1964 H. c. KENDALL ETAL 3,125,315

, RAILWAY CAR RETARDER coNTRoL SYSTEM 7 Sheets-Sheet 3 Filed June 2, 1953 JNVENTORS HQKENDALL AND JHUER JR.

BY l 7 THEIR ATTORNEY H. c. KENDALL ETAL 3,125,315

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United States Patent O 3,125,315 RAILWAY CAR RE'IARDER CONTROL SYSTEM Hugh C. Kendall and John H. Auer, Jr., Rochester, N.Y., assignors to General Signal Corporation Filed .lune 2,' 1953, Ser. No. 359,162 Claims. (Cl. 246-182) This invention relates to railway car retarder control systems, and more particularly pertains to a system using an electronic interferometer or radar device in a railroad classication yard for providing car speed data to associated equipment capable of controlling the retardation of cars as they pass through the various car retarders of such a yard.

In a classification yard, a string of cars is pushed in succession over the crest of a hump, and each car or cut of cars is allowed to roll under the influence of gravity down the hump and over a number of switches to a particular one of a number of destination tracks. In this way, the cars of a train are classified according to their intended destination.

The grade of the hump must be suicient to cause the lightest car to roll to the most remote destination in the classification yard. Heavier cars experience greater acceleration so that car retarders are required to reduce their speed to a suitable value by the time they reach their destination tracks. Each such car retarder comprises brake shoe beams disposed along the track rails which apply controllable braking pressure to the rims of the car wheels.

Inrolling down from the crest of the hump, the cars are switched from the main track to a plurality of branch tracks and then on to their nal destination. Car retarders are included in some of these branch tracks as Well as in tthe main track so that the speed of a car can be properly controlled for the conditions that relate to the particular branch track it will travel over. At certain locations, a plurality of retarders is provided rather than one retarder so that suicient retardation may be applied to heavy cars.

In classification yards, the practice generally has been to have an operator control manually the amount of braking force initially provided by each retarder on a particular car in accordance with the cars weight. A light car may require that little or no braking force be applied because its light weight may require that it leave the retarder with a fairly high speed. With greater car weights, the retarder operator must cause increasing braking force to be applied to the retarder, the retarder being effective when it applies maximum braking force to bring the speed of even the heaviest car to some desired low value.

The retarder operator is also required to release the retarder when he believes that the car speed is at a proper value. The desired leaving speed is affected by Various factors. The cars weight, for example, affects its further acceleration through the yard. Its intended destination affects the distance the car is required to roll and determines also the amount of curvature in its route, this latter factor having an effect because of the increased rail friction occurring when a car passes over curved track as opposed to straight track. The retarder operator is also required to take into account various other factors which affect the rolling resistance of a car such as windage, temperature, and the like.

In a system of this kind in which human judgment is depended upon to estimate actual car speed and also to ascertain what the speed of a particular car should ideally be as it leaves the retarder, any misjudgment by the retarder operator may result in unsatisfactory operation. A car may fail to reach its intended destination if it has been excessively retarded, or it may enter its destination track at too high a speed if it has not been sufficiently rice retarded and cause damage as it :couples to the other cars already in the destination track. Also, when several cars are simultaneously passing through the yard over diverse routes so that they occupy diflerent retarders at the same time, it becomes increasingly difficult for the operator to control the retarders properly.

To overcome these objections, a system has been provided in which the amount of braking force initially applied by a retarder is automatically selected in accordance with car weight as determined by a car weighing device -and in accordance with car speed as determined by suitable speed measuring apparatus. In this system, the time of release of each retarder is determined by the cars having reached a particular one of a plurality of different speed levels selected according to the weight and destination of the car and any other factors as may be required, with the car speed data being provided by appropriate speed measuring equipment. In this system, the car speed at which a retarder is released is automatically computed, but the automatic control can be modified by manual control when it is desired to compensate for various factors. It is also possible to cause the retarder control to revert entirely to manual operation when deemed necessary. A system of this general type for automatic control of the retarders in a classification yard is disclosed in the U.S. application Ser. No. 359,069 of N. B. Coley led on June 2, 1953.

It is proposed according to the present invention to provide a car retarder control system wherein electronic apparatus is employed that will supply distinctive outputs according to the instantaneous speed of a car as it passes through a car retarder to thereby provide car speed data for the automatic control of the car retarder to reduce the speed of the car to a computed release speed.

Another object of this invention is to provide speed measuring apparatus for railroad freight cars which will cause the selective picking up of a plurality of speed indicating relays according to the instantaneous speed of a car.

An additional object of this invention is to provide apparatus which is responsive to the difference in frequency between a transmitted continuous high frequency signal and the reflection of such signal as received from moving railroad cars in which each of a plurality of relays is selectively energized in response to a different preselected range of the difference frequency.

Another object of this invention is to provide a speed measuring apparatus for railroad classification yards employing the frequency shift of a reflected high frequency signal as compared to the frequency of a transmitted signal as the means for determining the speed of the reflecting car in which the plurality of preselected speeds for various cars leaving the retarder may readily be varied as required by manually or automatically operated means.

Other objects, purposes, and characteristic features of this invention will in part be obvious from the accompanying drawings, and in part pointed out as the description of the invention progresses.

In describing the invention in detail, reference will be made to the accompanying drawings in which like reference characters designate corresponding parts in the several views, and in which:

FIG. 1 illustrates in block form an automatic retarder control system comprising the speed measuring apparatus of the present invention;

FIGS. 2A and 2B when placed one above the other illustrate the detailed circuit of the speed measuring apparatus of this invention;

FIGS. 3A and 3B illustrate one form of the transmitting and receiving horn and associated antenna used in the speed measuring apparatus of this invention;

FIG. 4 illustrates certain wave forms representing voltages appearing in various parts of the system of this invention;

FIG. 5 illustrates graphically the manner in which the amplitude of the reflected signal varies with the position of the moving car;

FIG. 6 illustrates the means whereby the relationship between operation of the speed indicating relays and car speeds may be varied as required; and

FIG. 7 illustrates in detail retardation selection circuits indicated by block diagram in FIG. l.

To simplify the illustration and facilitate the explanation of this invention, the various parts and circuits which constitute the embodiment of this invention are shown diagrammatically and certain conventional illustrations are used. The drawings have been made to make it easy to understand the principles and manner of operation rather than to illustrate the specific construction and arrangement of parts that would be used in practice. The various relays and their contacts are shown in a conventional manner, and symbols are used to indicate connections to the terminals of batteries or other sources of electric current instead of showing all the wiring connections to these terminals. The symbols (B+) and (B-), for example, indicate connections to the opposite terminals of a source of voltage suitable for the operation of various electronic tubes and the like which is provided with a tap between the (B+) and (B-) terminals designated by the symbol for a ground connection.

Described briefly, the speed measuring apparatus of this invention comprises means for generating a continuous ultra-high frequency radio signal which is applied to a transmitting antenna placed in a horn reflector which may be of parabolic shape so as to produce the desired radiation pattern. The horn is preferably located between the track rails near or at the exit end of each car retarder, and the transmitted energy is directed towards approaching cars as they roll through the yard from the hump to their destination tracks.

The transmitting and receiving horn also includes a receiving antenna which receives energy that is transmitted from the transmitting antenna and then reflected from approaching freight cars. Because of the relative motion between the transmitting and receiving horn and the approaching freight cars, there is an apparent shift in frequency of the reected radio wave as compared to the transmitted wave according to the well-known Doppler effect. More specifically, for cars approaching the transmitting horn, the reflected wave is of a somewhat higher frequency than the transmitted wave. This difference in frequency between transmitted and received waves is proportional to the velocity of the approaching car.

The higher frequency reflected signal is applied to an electronic mixer. At the same time, a portion of the energy applied to the transmitting antenna is coupled directly to the receiving antenna and is also applied to the mixer. The mixer, therefore, receives two inputs; one being a portion of the transmitted signal and the other being the reflected wave which is of a somewhat higher frequency in accordance with the velocity of the approaching freight car. The mixer comprises a nonlinear circuit element so that a heterodyning action takes place and a beat signal, having a frequency equal to the difference in frequency of the two inputs applied to the mixer, is extracted from the mixer output. This beat frequency signal, which is proportional in its frequency to the car velocity, is then amplified and applied to pulse forming circuits. The resulting output pulses are effective, through their action on relay control units, to control a plurality of speed indicating relays which are selectively picked up or dropped away in accordance with a corresponding range of frequency of the beat signal. Consequently, each speed indicating relay is picked up when the speed of an approaching car exceeds some preselected value and remains picked up for all car speeds above this value. Thus, each relay contact unit may be considered to be an electronic high-pass filter in that a direct-current output effective to energize a relay is obtained whenever the input pulse rate exceeds a preselected value. In this way, the operated conditions of the speed indicating relays at all times provide an indication as to the speed range of an approaching freight car.

General Description 0f Apparatus FIG. 1 shows diagrammatically a stretch of track which is provided with a car retarder with the action of this retarder controlled through a car retarder mechanism CRM. The car retarder may be either of the electrically or pneumatically operated type. Near the exit end of the retarder is located a transmitting and receiving horn l0. This horn includes a transmitting antenna which receives energy from a continuous wave UHF oscillator 1l. A portion of the high frequency energy transmitted from the transmiting antenna is directly intercepted by a receiving antenna also included in the horn 10, and is applied to a crystal rectifier mixer I2. The receiving antenna included in the horn I0 also receives energy reflected from approaching freight cars, and this reflected energy is of a higher frequency according to the Doppler effect. This higher frequency signal is also applied to the crystal rectifier mixer 12. Because of the nonlinearity of this crystal rectifier mixer l2, a heterodyning action takes place which causes a signal equal in frequency to the difference in frequency between the two signals applied to the crystal rectifier mixer to be applied to a preamplifier i3.

Following amplification in the preamplifier 13, the beat frequency signal is applied to an amplifier and pulse former I4 which is effective to cause uniformly shaped pulses having a repetition rate corresponding to the frequency of the beat signal to be applied to the check relay control unit 15, high speed relay control unit 16, medium speed relay control unit 17, and low speed relay control unit 18. Each of these relay control devices other than the check relay control unit 15 responds to cause the picking up of the associated electromagnetic relay only when the output pulses of the amplifier and pulse former 14 occur at a rate above a corresponding preselected minimum value. Thus, the low speed relay control unit I3 will cause the relay LS to pick up only when the output pulses obtained from the amplifier and pulse former 14 occur at some preselected relatively low rate; whereas, the medium speed relay control unit 17 will cause relay MS to pick up only when the output pulses of the amplifier and pulse former 14 are received at some higher preselected rate. A still higher rate of pulse output from the amplifier and pulse former 14 must occur in order for the relay HS to be picked up by the high speed relay control unit 16. The check relay control unit 15, on the other hand, causes the relay CK to pick up whenever the pulses received from the amplifier and pulse former are at some discernible rate which is generally substantially below the rate required for the relay LS to pick up. In one embodiment of this invention, the check relay CK was picked up whenever the output pulse rate of the amplifier and pulse former exceeded the rate corresponding to a car speed of about one-half mile per hour.

The beat frequency output of the preamplifier 13 is supplied directly to the exit relay control unit 19. The exit relay control unit causes relay EX to pick up when the amplitude of the beat frequency signal reaches a saturating value, indicative of the fact that a car is in close proximity to the horn lll. When a car has passed over the transmitting and receiving horn It), the reflected signal and thus the beat frequency output of the preamplifier i3 diminishes rapidly in amplitude and causes the exit relay EX to drop away. This indication that a car has passed through the retarder allows resetting of various apparatus included in the retardation selection circuits 2f) as is describedl in the previously mentioned application of N. B. Coley.

In addition to the car speed data which is supplied to the retardation selection circuits by the various relays included in the speed detector 22, car weight data is supplied to the retardation selection circuits 20 from a weight detector WD which may be of any suitable kind.

The retardation selection circuits 2t) respond to the car weight and car speed data to provide the proper retardation control for the car retarder mechanism CRM. Manual control devices 23 may be provided to modify the car speed ranges for which the low, medium, and high speed indicating relays LS, MS and HS, respectively, are actuated.

The car retarder is illustrated in FIG. 7 as having a retarder operating mechanism CRM which can be controlled to selectively operate the retarder to any one of four different positions in accordance with the application of energy to the respective wires 0, 2, 3 and 4. These positions of the car retarder mechanism are respectively opened, light braking, medium braking and heavy braking. Although any suitable operating mechanism may be employed for operating the retarder to these different positions, a control system such as is disclosed in the U.S. patent to W. K. Howe No. 2,038,112, dated April 2l, 1936, may be employed. A multiple position control lever MCL is provided for selectively actuating the retarder manually to its different positions, or for permitting the retarder to be operated automatically when this lever is positioned as is illustrated in FIG. 7 to apply energy through its contact 34 to the contact 235 of relay CK. Relay CK is normally in its deenergized position, and energy is applied through the back contact 235 of this relay to wire number 4 to normally maintain the retarder in a closed position.

Upon passage of a car, the retarder is controlled in accordance with the energization of wires 2, 3 or 4 in accordance jointly with the car weight as registered by light, medium and heavy weight relays 1LW, 1MW and 1HW and in accordance with the speed as registered by relatively low, medium and high speed relays LS, MS and HS. The relays LS, MS and HS are generally all picked up when a car enters the retarder at a relatively high speed, and the relays drop away as the car speed is reduced in the sequence wherein relay HS is dropped iirst, relay MS second, and relay LS last.

If a car approaching the retarder is a medium weight car, and if it is approaching at a speed to cause the relays LS, MS and HS to be initially picked up, as will be hereinafter considered more specifically, the control wire 3 becomes energized to apply medium braking to the car. The relay CK is in its picked up position at this time so that energy is removed from the retarder control wire 4, and the control wire 3 becomes energized by a circuit including contact 234 of lever MCL in its lefthand position, front contact 235 of relay CK, back contact 256 of relay 1HW, front contact 257 of relay lMW, front contact 260 of relay MS, and front contact 261 of relay HS. As the speed of a car is reduced so that the relay HS becomes dropped away prior to the dropping away of relay MS, the shifting of contact 261 of relay HS removes energy from wire 3 and applies energy to wire 2 to operate the retarder to a light braking position. When the speed of the car is reduced so as to cause the dropping away of relay MS, the shifting of its contact 260 opens the circuit for the energization of wire 2 for the control of the retarder and applies energy to wire 0 so as to open the retarder in accordance with the speed of the car having been reduced to the predetermined release speed for that car in order that it may re-ach its destination at the desired velocity.

Having described a specific example of the selection of different degrees of retardation for a medium weight car, it is to be understood that similar means is provided for selecting the degree of retardation for a heavy Weight car in accordance with contact 256 of relay 1HW, and for a light weight car in accordance with contact 258 of relay lLW. The circuits are described more in detail for the selective control of the degree of energization of the retarder in accordance with weight classification in the above mentioned Coley application Ser. No. 359,069, led lune 2, 1953. Reference can be readily made to this prior Coley specication in that the circuits involved in the selection of the degree of retardation in the present application bear reference characters corresponding to those used in the Coley specification except that they are preceded by the numeral 2.

Operation of Oscillator and Antenna System The continuous Wave UHF (ultra high-frequency) oscillator 11 is shown in FIG. 2A as including a cavity resonator 24. The resonator may be of the re-entrant type employing a tube 25 commonly known as a lighthouse tube. Such a resonator with its associated tube is shown in Fig. 7.1 on page 173 of the book Klystrons and Micro-Wave Triodes7 which comprises vol. 7 of the Radiation Laboratory series, published by McGraw-Hill Company. As shown in FIG. 2A, the control grid is connected through a resistor 26 to ground, and the plate is connected through a current-limiting resistor 27 and then through a choke coil 28 to the (B+) voltage source. The capacitor 29 shunting coil 28 cooperates with this coil to provide additional ltering of the plate voltage supply for tube 25.

The transmitting and receiving horn 10 may be, as illustrated in FIG. 3A, of the kind known as a pillbox, being constructed of a conductive material and having a reflecting back surface 31 that follows a parabolic curve so that a transmitting antenna 32 placed at the focus of the parabola will cause the radiated energy to be transmitted in a relatively confined beam along its axis. Radiofrequency energy reflected from a moving freight car and intercepted by the horn 10 is reilected from the parabolic back face of the horn 10 to the receiving antenna 33 which is also located at the focus of the parabola.

The receiving antenna 33 receives a relatively small portion of the energy radiated from the transmitting antenna 32 and reflected from the back surface 31. Because the surface presented by the receiving antenna 33 is small as compared to the area of the open front portion of the horn 10, only a small portion of the energy radiated from the transmitting antenna is intercepted by the receiving antenna as this energy is reflected from the parabolic back surface and escapes through the front of the horn. This tends to provide the desired ratio in amplitudes between the two signals received by the receiving antenna for proper mixing action, the one being a portion of the transmitted signal and the other energy reflected from the approaching freight cars and intercepted by the horn.

As shown in the cross sectional view of FIG. 3B, the transmitting antenna comprises what is known as a folded quarter-Wave ground plane antenna. The circular disc 5S forms the ground plane and is fastened to a sleeve 59. Inside the sleeve 59 is an insulating bushing 60 having a hollowed core in which is inserted the probe 61. The probe 61 is threaded at its upper end into the bent over portion 62 of the sleeve 59. The cavity resonator 24 may be fastened on the horn 10 directly below the transmitting antenna 32 by the bracket 63 in such a manner that the probe 61 can be inserted directly into the cavity and thus allow the coupling of high frequency energy directly to the transmitting antenna. The outer surface of the sleeve 59 is threaded over its lower portion to permit it to screw into a boss 64 in the cavity 24. In this way, the coupling of the probe 61 to the cavity 24 may be adjusted by merely rotating the threaded sleeve in the boss 64 so as to vary the amount by which the lower end of the probe extends into the cavity 24. The desired coupling adjustment is maintained by the lock nut 155. The clearance hole 156 in the horn is suiciently large to ensure that there is no electrical contact between the antenna and the horn. The use of Va ground plane as provided by the disc 58 permits varying the coupling of the probe to the cavity without varying the distance by which the folded quarter wave antenna extends above its associated ground plane.

The receiving antenna 33 is also a quarter-wave antenna with fthe upper surface of the horn acting as its counterpoise. As shown in FIG. 3B, this antenna comprises a cylindrical radiator 157 having a terminal 153 connected therewith, with the upper end of the radiator being inserted into a hole provided in the insulating washer 159. This washer is held in place in the sleeve 164i which has its Voutside surface threaded so as to iit into a threaded hole in the upper surface of the horn 11i. T he sleeve 16d is provided with an opening into which fits the crystal rectier 35 shown diagrammatically in FIG. 2A. Thus, one end of this crystal 35 is connected to the upper end of the radiator 157, which radiator is insulated from the sleeve 16@ by the insulating washer 159. A nut 162, threaded both on the inside and outside, fastens `over the upper threaded portion of the sleeve 161i to thereby lock the sleeve in the desired position with respect to the upper surface of the horn 10. A cap 163, threaded on the inside screws onto the nut 162 and causes the spring 164 to exert a pressure on the crystal 35 so as to maintain it in proper contact with the radiator 157, and also ensure its upper end being connected to the upper surface of the horn 1t) which is at ground potential. The signal from the receiving antenna 33 is coupled to the preamplifier 13 by means of a connection made to the terminal 15S.

Although a cavity resonator is shown in FIG. 2A as being included in the continuous wave UHF oscillator 11, obviously other kinds of high frequency oscillators may as well be used.

A portion of the high frequency energy radiated from the transmitting antenna 32` included in the transmitting and receiving horn 1t) of FIG. 3A is reected from the parabolic surface of the horn and is then directly intercepted by the receiving antenna 33 also included in the same horn in FIG. 3A. The high frequency energy radiated from the horn is directed by the horn over the path to be travelled by an approaching car. -It is `desirable that the path of the radiated energy be confined rather closely to the associated track so that movement of cars in adjacent tracks will generally not cause an improper output [from the speed detecting apparatus. In one embodiment of this invention, the beam of radiated energy was confined to a path having an angle in the horizontal dimension of about degrees, with the angle in the vertical path being approximately 30 degrees.

The location of the transmitting and receiving horn 1) and the amount of power supplied to the transmitting antenna 32 should be such that the reflected signal 'from a car will be of suiiicient strength to ascertain the speed of a car before it enters the retarder as well as when the car is passing through the retarder. When the car has passed entirely out of the retarder, however, the reflected signal should be so diminished in amplitude that the exit relay control unit 19 will allow the relay EX to drop away so as to restore the retardation selection circuits 20 and allow the retarder to be controlled for the next car. Consequently, in one specific embodiment of this invention, it was found that placement of the transmitting and receiving horn 10 between the track rails and about ten feet in from the leaving end of the retarder produced the `desired results. Secondary reflections occur even after the car has passed over the horn so that a beat frequency signal is still received at such time as shown graphically in FiG. 5. When the car has reached a distance of about ten feet behind the horn 10, the reflected signal has so diminished that the exit relay EX drops away. Consequently, placing the horn `10 about ten feet in ifrom the leaving end of the retarder causes the relay EX to drop away at about the time the car clears the retarder. =`In this embodiment previously mentioned, the apparatus was effective to determine car speed for cars about iifty feet in 4front of the horn 10 so that for a retarderof about forty-five foot length, the car speed was registered when the car was approximately fifteen feet in advance of the retarder. These specific dimensions are mentioned merely for purposes of illustration and may readily vary over a considerable range depending on conditions.

Mixer and Preamplifer As each car approaches the car retarder, it causes some of the high frequency enengy radiated from the transmitting and receiving horn 10 to be reected back to the horn. The receiving antenna 33 (see FIG. 3A) intercepts this reflected energy and applies it to the crystal rectiiier mixer 12 of FIG. 2A. As previously mentioned, the receiving antenna 33 also intercepts directly some of the energy transmitted from the transmitting antenna 32. The reflected ener-gy has a frequency which is slightly different from that of the radiated energy when such energy .is reected from a surface having a component of velocity toward or away from the horn 10. This socalled Doppler frequency shift causes the crystal rectitier mixer 12 to receive two signals from the receiving antenna differing in frequency by the amount of the Doppler shift which is proportional to the velocity of the approaching yfreight car. The rectifying effect produced by the crystal 35 of FIG. 2A, which is shunted by the resistor 36, causes a heterodyning action with the result that the beat or `dierence frequency is applied through the coupling condenser 37 to the control grid of tube 38 included in the preamplifier 13. Because the speed of freight cars through a classification yard is 0f a relatively low value, the beat lfrequency applied to the grid of the tube 3S is of a correspondingly low value also. Thus, for an oscilla-tor frequency in the region of 2,500 megacycles per second, the beat frequency will vary from about 30 to 11() cycles per second for car speeds varying from 4 to `15 miles per hour.

Tube 33 is operated as a class A amplifier with cathode self bias being provided by the cathode resistor 39 which is shunted by capacitor 40 for the range of frequencies required to be amplified. Grid leak resistor 41 is connected from the control grid to ground, and the screen grid is enengized lfrom the (B+) voltage supply through a dropping resistor 42. The screen grid is by-passed for the range of vfrequencies required to be amplied by the condenser 43. The -beat frequency signal appearing across the plate load resistor 44 is capacitively coupled through capacitor 45 and the gain control potentiometer 46 to the control grid of another class A amplifier tube 17.

The output plate voltage of the tube 47 appearing across load resistor 43 (see FIG. 4, line A) is applied through coupling capaci-tor 49 to the control grid of triode amplifying tube 5@ which has its control grid connected through the grid leak resistor '51 to ground. Although the control grid of tube Sti is normally at ground potential, the plate current can be further increased in response to positive half-cycles of the beat frequency input. As a result, clipping of the positive half-cycles does not occur until a car is fairly close to the antenna so that the reflected signal is of larger amplitude.

The plate vol-tage of tube 5t) is applied directly to the [grid of cathode follower tube `53. The beat frequency output appearing across cathode load resistor 54 (see FIG. 4, line B) is then fed through the coupling capacitor 55 to the input circuit of tube 56 included in the amplier and pulse former `14, and also to the input circuit of tube 57 included in the exit relay control unit 19 shown in FIG. 2B.

Amplifier and Pulse Former The beat frequency signal applied to the amplier and pulse former 14- from the output of the preamplifier 13 appears across the potentiometer which has its variable tap connected through the coupling capacitor 66 to the control grid of pentode amplifier tube 56. This tube 56 is class A operated, receiving its self-bias through the effect of the cathode resistor' 68 and its associated by-pass capacitor 69. The control grid of tube 56 is connected to ground through grid leak resistor 70. The screen grid is energized through the resistor 71 and is also by-passed to ground through capacitor 72. The plate of this tube 56 is connected through load resistor 73 to the (B+) voltage source and is also connected through capacitor 74 to ground. Capacitor '74 causes a reduction in the high frequency response of the amplier by providing a shunt path to ground for high frequencies. Since the beat frequency signal to be amplitied is of a low frequency as already mentioned, the reduction of high frequency response has substantially no effect upon the amplitude of the desired signal but is very effective in eliminating high frequency noise components, resulting in a substantial increase of the signal-to-noise ratio of the system.

The beat frequency input applied to the control grid of tube 56 causes an output across its plate load resistor 73 substantially as shown at line C of FIG. 4. This output of tube 56 is applied through coupling capacitor 75 and grid-current-limiting resistor 76 to the control grid of amplifier tube 77. A voltage dividing network is provided by the resistors 78 and 79 which are connected from the (B+) source to ground. This network causes a positive voltage to be applied through resistor 80 to the junction of capacitor 7S and resistor 76 or point 67. The tendency of the control grid of tube 77 to be driven positive with respect to its grounded cathode because of this positive voltage is overcome by the passage of a small amount of grid-cathode current through the relatively large resistor 76 so that the grid-cathode potential of the tube 77 is prevented from becoming positive and thus remains at about zero voltage.

In response to each negative half-cycle of the beat frequency signal obtained from the plate of tube 55, the voltage at the junction of resistor 76 and capacitor 75 is decreased in value. When the negative half-cycle has reached suicient amplitude to overcome the positive bias voltage at point 67, the control grid becomes negative with respect to ground potential. Further decrease of this voltage causes tube 77 to become nonconductive. Since tube 'I7 is abruptly made fully nonconductive by each negative half-cycle, unwanted noise voltages that may be present can have no further effect on the output of this tube. Consequently, the output of this tube obtained across load resistor 81 comprises substantially only positive-going pulses occurring at a rate equal to the frequency of the beat signal. The abruptness with which tube 77 is changed from a fully conductive to a fully nonconductive condition because of its large amplitude input pulses, causes its positive-going output pulses to have relatively steep leading and trailing edges as shown in line D of FIG. 4.

With tube 77 normally in a fully conductive condition, the voltage drop appearing across its plate load resistor 81 causes its plate voltage to be at a relatively low value. The plate of tube 77 is connected through the differentiating capacitor 82 to the control grid of triode tube 83. The control grid of this tube 83 is connected through a resistor 84, which is of relatively large value, to the (B+) voltage source. Any tendency of the control grid of tube 83 to become positive in voltage with respect to its ground and cathode results in a flow of grid-cathode current through the resistor 84 in the same way as was described in connection with tube 77 so that the grid of tube 83 is actually at about ground potential. Consequently, With the grid of tube 83 at approximately ground potential and a low voltage appearing on the plate of tube 77, the capacitor 82 has only a slight charge.

When tube 77 has its control grid driven negative on a negative half cycle of the beat frequency signal supplied by the output of tube 56, the plate voltage of tube 77 rises abruptly in amplitude. This rise in plate voltage causes the condenser 82 to charge through the grid-cathode circuit of tube d3. Because of the relatively small grid-cathode resistance of tube 83 as compared to the plate resistor 31 of tube 77, the grid-cathode voltage of tube S3 experiences only a very slight voltage increase as the plate voltage of tube 77 first rises. Also, this charging circuit for capacitor 82 has a relatively short time constant so that capacitor 82 is quickly charged.

At the end of its negative-going input pulse, tube 77 again becomes conductive and its plate voltage abruptly drops in value. Capacitor 32 now discharges through resistor 84 and the plate-cathode circuit of tube 77. The momentarily large iiow of current through resistor 84 causes the grid of tube 83 to be driven abruptly negative with respect to ground with this voltage rising towards its normal zero value as condenser S2 becomes discharged to its new steady state value at a rate determined by the time constant of the discharge circuit. During the interval that tube b3 is cut oif by the negative voltage applied to its control grid, its normally low plate voltage rises abruptly to substantially the (B+) level (see line E, FIG. 4) because of the cessation of plate current flow through the plate resistor 8S. The resultant charging of capacitor 86 causes a positive pulse to appear on the control grid of gas discharge tube 57.

The control grid of tube 37 is connected through a grid current limiting resistor 8% and through the resistor 89 to the (B+) source. The negative voltage that is thus normally present on the grid of tube 37 causes it to remain in a nonconductive condition. The positive voltage pulse that is applied to its control grid for each half-cycle of the beat frequency wave causes tube 37 to become conductive.

The gas discharge tube 87 is provided with a selfquenching means comprising the capacitor 90. When ytube 87 is in its normal nonconductive condition, there is no plate current flow through the plate load resistor 91 so that the plate voltage is at substantially the (B+) voltage level. The capacitor @il connected between the plate and ground is thus charged to this high voltage. When tube 87 becomes conductive, the capacitor 9@ quickly discharges through the plate-cathode circuit of the tube. At the same time, the plate voltage is reduced to a low value by the voltage drop appearing across the resistor 91. It is believed that some slight inductance in the circuit, possibly in the plate and cathode connections cooperates with the capacitance provided by the capacitor to result in some oscillations of the plate voltage when the tube becomes conductive and the plate voltage is at its loW value. Such an oscillation occurring subsequent to the termination of the grid pulse which caused the tube to fire is believed to reduce the plate-cathode potential momentarily below that required to maintain the tube conductive so that tube S7 is extinguished. Upon thus being extinguished, the plate voltage rises at a rate as determined by the time constant associated with the charging of capacitor 90. In this way, the gas discharge tube 87 is made conductive for each cycle of the beat frequency signal that has an amplitude above some preselected minimum value with the tube 87 being effective to extinguish itself following each such firing so that there is applied to the wire 95 from the plate of tube 87 a series of negative-going voltage pulses substantially as illustrated in line F of FIG. 4.

Operation of Speed Indicatif/Lg Relay Control Units The negative-going pulse output of the amplifier and pulse former 14 is applied over wire 95 to the input of each of the various relay control units shown in FIG. 2B except the exit relay control unit 19 which receives its input directly from the preamplifier 13. In the description of the operation of these various relay control units specific voltage values will occasionally be mentioned to facilitate the description. The citing of such specific voltage values is in no way intended to limit the scope of the invention to such values because the principles of this in- 1 1 vention apply equally well over wide ranges of values of circuit components and voltages.

As shown in FIG. 2B, the hich speed relay control unit 16, medium speed relay control unit 17, and low speed relay control unit 1S are alilte except as to the Values of certain circuit components so that the description of the operation of these units will be described in connection with a typical one, namely the high speed relay control unit 16.

Each relay control unit such as the high speed relay control unit 16 comprises two diode tubes such as the diodes 96 and 97, a normally conductive triode tube $8, and a normally non-conductive relay control tube 99. This latter tube includes in its plate circuit the high speed relay H31 so that with tube 39 normally nonconductive, the relay H81 is dropped away.

The control grid of tube 93 is connected through resistor 100 and resistor 101 to the (B+) voltage source. The llow of grid-cathode current of tube 98 through the relatively large resistance provided by the resistors 100 and 101 produces a voltage drop that causes the control grid of tube 9S to be substantially at the voltage of its grounded cathode. The potential at the junction of resistors 100 and 101, however, is at some preselected volage level between ground and the level of the (B+) voltage supply and may, for example, be about 50 volts positive with respect to ground. rthe capacitor 1d?. is thus normally charged to this positive 50 volt potential.

The cathode or" diode tube 96 is connected through a capacitor 103 to ground and is also connected to a tap on the potentiometer 10d which is connected between (B+) and ground. The potentiometer .l-tis adjusted to provide a preselected voltage level to the cathode of diode 96 according to the particular car speed at which the high speed relay control unit 16 is to cause the relay H51 to be picked up. As will subsequently become clear, the potentiometer 105 included in the medium speed relay control unit 17 is adjusted to provide a somewhat lower voltage level for the cathode of diode 106 than is provided for the cathode of the diode 95. Similarly, a still lower voltage level is provided for the cathode of diode 107 included in the low speed relay control unit 1S by the adjustment of the potentiometer d. lt will be assumed in the present discussion that the potentiometer 104 causes a voltage of 200 volts to be applied to the cathode of the diode tube 96 included in the high speed relay control unit 16.

Under the normal conditions now being described, the plate of diode 97 is at +50 volts. The cathode of this diode 97 assumes a potential between this 50 volt level and the 200 volt clamping voltage level. lt will be assumed for the purposes of this discussion that the cathode Voltage of diode 97 is initially at 50 volts. The diode 96, having 200 volts applied to its cathode, is normally nonconductive so that there is no current ow through resistor 115 with the result that the plate of diode 96 is also substantially at +50 volts. Wire 95, on the other hand, is connected to the plate of the normally nonconductive gas discharge tube 87 so that it is at substantially the (B+) voltage level. Capacitor 116 which connects wire 95 to the plate of diode 96 is, therefore, charged to a substantially high voltage; with a (B+) voltage of +300 volts, capacitor 116 would be charged to about 250 volts.

When a car approaches sufciently close to the horn 10 located between the traclr rails, the reilected energy becomes suiciently strong to cause the beat frequency signal to repetitively iire the gas discharge tube d'7 in a manner already described. When tube 87 is made conductive the rst time, a short time constant path is provided for the discharge of capacitors 116 and 102. This discharge circuit includes the capacitor 102, diode 97, the relatively low resistance of resistor 115, the capacitor 116, and the plate-cathode circuit of tube 37. Resistor 115 limits the maximum current passing through both diode 97 and the gas discharge tube 87. Capacitors 102 and 116 are thus,

effectively connected in series through the plate-cathode circuit of tube 37. The larger voltage across capacitor 116 as compared to that across capacitor 162 causes a transfer of charge to capacitor 102 with a resulting decrease of voltage at the upper terminal of this capacitor. Since the capacitor 102 has a considerably greater capacitance value than the capacitor 116, the charge transfer is accompanied by a relatively small change of Voltage across capacitor 102. In one particular embodiment of this invention, the capacitor 102 had a value of one microarad, whereas the capacitor 116 had a capacitance of .01 microfarad. Under such circumstances, the voltage decrease across the normally charged capacitor 102 is about one hundredth of the voltage drop appearing at the plate of tube $7 of FIG. 2A.

Upon the termination of the negative-going pulse derived from the plate of tube 87, the voltage applied to wire rises exponentially toward the (B+) voltage level. As this voltage starts to rise, the voltage at the plate of diode 96 also starts to rise, thereby causing the cathode of diode 17 to become positive with respect to the plate of this diode so that the diode 97 immediately becomes nonconductive. With the continuing rise in voltage on wire 95', the voltage at the plate of diode 96 rises correspondingly since the capacitor 116 can now not become charged as a result of the nonconductivity of both the diodes 96 and 97. However, when the voltage on wire 95 exceeds the +200 volt clamping voltage assumed to be applied to the cathode of diode 96, this diode becomes conductive and allows the capacitor 116 to charge. As the wire 95 rises in voltage and finally reaches the (B+) level which may be at +300 volts, the plate of the diode 96 is prevented from exceeding +200 Volts by reason of the clamping action of the diode 96 so that capacitor 116 becomes charged to this 100 volt difference in potential.

The charging current for capacitor 116 which passes through diode 96 is provided mostly by the capacitor 103 which is normally charged to the clamping voltage selected by potentiometer 104. This capacitor is of a suliiciently large value of capacitance to ensure that its voltage will decrease only slightly when it gives up charge for the charging of capacitor 116. Between input pulses, this capacitor 103 is again fully charged from (B+) through potentiometer 104. The advantage provided by the use of capacitor 103 is that it tends to prevent a drop in the clamping voltage that would otherwise occur as a result of the ow of charging current for capacitor 116 through the resistance of potentiometer 104.

When the gas discharge tube S7 in FIG. 2A is again made conductive on the following cycle of the beat frequency signal, the voltage on wire 95 immediately drops once more from its assumed +300 volts to a voltage of approximately +20 volts. In response to this voltage decrease, the voltage at the plate of diode 96 immediately drops below 200 volts to thereby cause the diode 95 to become immediately nonconductive. If it is assumed that the first firing of the gas tube 87 caused the voltage across capacitor 102 to drop from its normal value of 50 volts to a new value of approximately 47.5 volts, then it will be seen that the negative pulse on wire 95 must cause the plate of the diode 96 to drop in voltage from its initial +200 volts between pulses to slightly below 47.5 volts in order for the diode 97 to become conductive. Thus, the rst 152.5 volt drop at the plate of diode 96 occurs with diode 97 as well as diode 96 nonconductive so that the charge across capacitors 116 and 102 remains substantially unchanged. Only for the remainder of the assumed 280 volt pulse, or 127.5 volts, is diode 97 conductive. Of this voltage drop, again only about one percent is elective on capacitor 102, the rest of the pulse being effective to reduce the voltage across capacitor 116. I

In a way similar to that which has just been described, each tiring of gas tube 37 results in a further discharge of the capacitor 102; and when the condenser is fully discharged, additional negative pulses on wire 95 cause the capacitor 102 to charge with a negative voltage, thereby causing the control grid of tube 98 to assume a negative potential with respect to its grounded cathode.

In the normal, steady state condition, the capacitor 102 is described as being charged to approximately +50 volts. As described, each negative-going pulse on wire 95 causes a decrease in voltage at the upper terminal of this capacitor 102. Between these input pulses, however, the capacitor 102 tends to be recharged toward its normal steady-state voltage. The time constant of this charging circuit is affected by the values of the capacitor 102 and resistor 101 and since the resistance in this charging circuit is preferably of a large value of resistance, the capacitor 102 can charge only slightly between successive input pulses.

As already described, the negative-going input pulses must cause the voltage at the plate of diode 96 to be reduced from the voltage at which this plate is clamped as determined by the setting of the potentiometer 104, to a voltage somewhat less than the voltage appearing at` the plate of diode 97 before the diode 97 will become conductive and allow a further decrease in voltage to take place at the upper terminal of capacitor 102. Therefore, merely by changing the setting of the tap on potentiometer 104 so as to vary the voltage at which the plate of diode 96 is clamped, it is possible to vary the degree by which each input pulse is effective to change the voltage across capacitor 102.

If the tap on the potentiometer 104 is adjusted to provide a high cathode voltage for diode 96, then each negative-going input pulse must lower the voltage at the plate of diode 96 from such high voltage to the lower voltage appearing at the plate of diode 97 before the diode 97 will become conductive and allow the remainder of the negative input pulse to alect the voltage across capacitor 102. By lowering the voltage on the diode as is done with the diode 106 in the medium speed relay control unit 17 and even more so with respect to the diode 107 in the low speed relay control unit 18, it is possible to cause a greater portion of each input pulse to be elfective upon the capacitor with the result that the capacitor 102 changes its voltage by greater increments for each input pulse.

The voltage which the capacitor 102 reaches after a plurality of input pulses has been efrective on the high speed relay control unit 16 also affects the amount by which each negative pulse can further change the voltage across this capacitor 102. Initially, each negative-going voltage pulse on wire 95 must cause the plate voltage of diode 96 to be lowered from the voltage at which this plate is clamped to a level below the 50 volt level at the plate of diode 97 before the diode 97 will become conductive. After a succession of input pulses has been received, and the voltage across capacitor 102 is reduced to volts, for example, then each input pulse must cause the plate voltage of diode 96 to be reduced from its clamped level to below +5 volts rather than +50 volts before the diode 97 will become conductive.

In addition, the more the voltage at the upper terminal of capacitor 102 is reduced from its normal steady-state value of an assumed +50 volts, the greater is the amount by which this capacitor is recharged between each successive input pulse. When, for example, the input pulses nally cause the voltage at the upper terminal of capacitor 102 to be reduced to -10 volts, a substantially greater amount of charge will be replaced on this capacitor between pulses than if this capacitor is charged to say +40 volts.

A state of equilibrium is eventually reached for each pulse rate when the amount by which the voltage at the upper terminal of capacitor 102 is reduced by each negative pulse equals the amount by which this same voltage is increased between successive negative pulses. The voltage on capacitor 102 for this equilibrium condition is dependent on the pulse rate. F or example, if after equilibrium conditions have been reached, the input pulse rate is increased, the rate at which capacitor 102 loses charge in response to the input pulses will increase, causing a reduction in voltage at the upper terminal of this capacitor. The capacitor voltage will decrease, with an accompanying increased rate of charge between pulses until a new equilibrium condition is again reached at which the charge gained by this capacitor between input pulses equals the charge lost in response to input pulses. Consequently, for each pulse rate applied to the high speed relay control unit 16, there is a corresponding voltage appearing at the upper terminal of capacitor 102 and applied to the grid of tube 98. From the description that has been given, it will be clear that this voltage at which equilibrium occurs is dependent upon the voltage at which the diode 96 is clamped since this determines the extent to which the input pulses are to be effective on capacitor 102. Thus, the potentiometer provided for each speed relay control unit may be adjusted so that for some preselected speed level, the pulses occurring on wire will result in tube 98 (or the corresponding tubes 118 or 119) becoming nonconductive.

When tube 98 is in its normal conductive condition, the ow of plate current through its plate resistor results in a. low plate voltage for this tube. Thus, the voltage divider comprising the series resistors 111 and 112 connected between this plate and the (B-) potential source causes a cut-olf grid-cathode voltage to be applied to tube 99. With tube 99 cut-off, the relay HSI is dropped away. When tube 98 becomes nonconductive, the voltage at the plate of this tube rises,v thereby raising the grid voltage of tube 99 sufficiently to make this tube conduct with the result that relay HSI picks up. A momentary rise of voltage at the plate of tube 98 will not cause tube 99 to become momentarily conductive because of the elect of capacitor 113 connected between the grid of tube 99 and ground. The high plate voltage of tube 98 resulting from its being nonconductive must persist for some time in order for capacitor 113 to change its voltage and allow the grid of tube 99 to be raised in voltage.

Only a relatively small variation in voltage across capacitor 102 is required to vary the grid potential of tube 9S sufficiently to change this tube from its normally conductive condition to a fully nonconductive condition. As a result, tube 99 will likewise have its condition changed from cutoff to full conduction in response to such slight change in voltage across capacitor 102. This means that if relay HSI picks up for some predetermined car speed, it will drop away when the car speed falls below this predetermined value by only a very slight amount. As a result, the braking effect exercised by any retarder can be both initially selected and removed for about the same pre-established car speeds rather than at different speeds as would occur if relay HSI were to drop away at a lower speed than that which causes it to pick up.

In FIG. 2B, the diode 96 included in the high speed relay control unit 16 is connected to a tap on potentiometer 104 so that a variable positive voltage may be applied to the cathode. A similar arrangement is provided for the diodes 106 and 107 included in the medium and low speed relay control units, 17 and 18 respectively. It may be desirable, however, to control the voltage at the cathode of these diode tubes in the manner shown in FIG. 6. This circuit organization facilitates the varying of the car speeds for which the various speed indicating relays are actuated in response to external control, either manual or automatic. In this FIG. 6, only portions of the various speed relay control units are shown. For example, that portion of the high speed relay control unit 16 cornprising capacitor 116, diode 96,' and capacitor 103 is illustrated, the remainder of this circuit organization being as shown in FIG. 2B.

In FlG. 6, the cathode of diode 96 is shown connected to a tap on potentiometer 170. This potentiometer 170 has its upper terminal connected through another potentiometer 171 to the (B+) voltage source. The diodes 196 and 1117 have their cathodes similarly connected to the taps on the potentiometers 172 and 173.

The lower terminals of the potentiometers 17), 172, and 173 are connected through a series circuit comprising potentiometer 174, back contact 177 of relay CR, potentiometer 175, and the N or normal position of switch 178, to ground. The voltage that is applied, therefore, to the cathodes of the diode tubes 96, 196, and 107 is dependent upon the setting of the taps on the respective potentiometers 171D, 172, and 173, the variable resistance provided by potentiometers 171, 179, and 1819, respectively, and the resistance presented by potentiometer 175. These potentiometers are adjusted to provide the required voltage on the cathode of these diodes that will cause the associated speed indicating relays to be actuated for car speeds above the normal preselected values.

The curve relay CR is controlled in accordance with the route to be taken by the car through the classication yard and is picked up whenever the car is to travel over a route having a relatively large amount oi curvature. The relay CR can be controlled, for example, by a circuit organization such as is disclosed for the control of relay 3D1 of FIG. 4 in the Patent No. 2,194,353, issued March 19, 1954, and assigned to the same assignee as the present application. The picking up of relay CR opencircuits the shunt around potentiometer 174 so that the resistance between point 131 and ground is increased. dependent upon the setting of potentiometer 174. As a result, the voltage applied to the cathode of diodes 96, 1136 and 107 is somewhat increased, resulting in the respective speed indicating relays being actuated at somewhat higher car speeds than normal. In this way, the picking up of the curvature relay CR allows a car to be released from the retarder at a somewhat higher speed so as to compensate for the increased curvature in its intended route.

If the operator desires that a car leave the retarder at a somewhat lower than normal speed to compensate for various factors, he operates the switch 178 to the L or low position. This causes the tap on potentiometer 175 to be connected through the switch 178 to ground with the result that the resistance between point 181 and ground is decreased and a lower voltage appears on the cathode of the diode tubes. This lower cathode voltage causes the associated relays to be actuated at somewhat reduced car speeds.

If the switch 178 is operated instead to the high or H position, the shunt normally provided around the potentiometer 176 is removed so that additional resistance is inserted in the circuit between point 131 and ground, dependent upon the setting of the potentiometer 176. This results in a somewhat higher voltage being applied to the cathodes of the diode tubes so that the respective speed indicating relays are actuated at somewhat higher car speeds.

As a result, the circuit means shown in FIG. 6 makes it possible to vary the car speeds for which the various speed indicating relays are actuated in accordance with either manual or automatic control, or both simultaneously, thereby resulting in a greatly increased exibility of operation of the system.

Operation of Check Relay Control Unit The circuit organization provided for the control of the check relay CK causes this relay to be picked up for substantially all car speeds providing only that the car is within range of the system. Consequently, the check relay CK may be used not only to check the operation of the speed determining apparatus but also to provide an indication of very low speed of approaching cars. When the check relay CK is energized but the low speed relay 155 LS is dropped away, for example, an indication is provided that a car is approaching but is travelling at a speed lower than that which will cause relay LS to pick up. This condition of the relays CK and LS can then be made effective on the retardation selection circuits 2i) to cause the car retarder to be opened.

The check relay control unit 15 also receives negativegoing pulses from wire 95, and these pulses are applied to the plate of diode 125 through the capacitor 126. The plate of diode 125 is connected through a resistor 127 to the cathode of diode 128, and the plate of this diode 128 is connected to the control grid of triode tube 129 and to the parallel combination of capacitor 130 and resistors 137 and 131. The plate output voltage of tube 129 controls the conduction of the tube 132 which is normally biased to a nonconductive condition because its control grid is connected through resistor 133 to the (B-) source of voltage. The relay CK connected in the plate circuit of tube 132 is, consequently, normally dropped away.

From this description of the check relay control unit 15, it is clear that this circuit organization is very similar to that provided in the various speed indicating relay control units such as the high speed relay control unit 16 previously described. One difference is that the control grid of tube 129 is connected through resistor 137 to the junction of the voltage divider resistors 13S and 131 connected in series between (B+) and ground. The positive voltage that is applied to the lower terminal of resistor 137 by the voltage divider is just sullicient to cause this tube to be normally in a fully conductive condition. The voltage drop normally appearing across plate load resistor 134 causes a relatively low voltage to appear at the plate of tube 129 so that the voltage appearing at the junction of the voltage dividing resistors 135 and 133 connected between this plate and the (B-) source causes tube 132 to be normally nonconductive.

Another difference relating to the check relay control unit 15 as compared to the high speed relay control unit 16 is that the cathode of diode 125 is grounded rather than being connected to a positive voltage tap on a potentiometer. From the description of the high speed relay control unit 16 that has been given, it will be clear that the elect of grounding the cathode of diode 125 is to clamp the plate of this diode at ground potential so that the full amplitude of each negative-going input pulse on wire is effective to negatively charge the capacitor 130 rather than just a portion of such pulses. Thus, by connecting the cathode of diode directly to ground, the potential at the plate of diode 125 need be lowered only from its maximum zero voltage to a value slightly below that appearing at the plate of diode 128 in order for this latter diode 128 to become conductive and allow the capacitor 131) to receive an additional negative charge. In this way, the negative input pulses appearing on wire 95 are more effective to lower the Voltage at the upper terminal of capacitor than they are in lowering the voltage at the upper terminal of capacitor 102 in the high speed relay control unit 16. Consequently, the voltage at the control grid of tube 129 is lowered to a level to cut olf this tube with a considerably lower rate of negative input pulses on wire 95 than is required to cut oil the tubes 98, 113 or 119 included in the respective relay control units 16, 17 and 18.

Another factor alectng the ability of the negative input pulses to cut olf the tube 129 results from the fact that the capacitor 1341 is initially not charged to a positive voltage but is instead normally in a substantially discharged condition. The capacitor 192 included in the high speed relay control unit 16 is normally charged to a positive voltage as already explained so that a higher rate of input pulses is required to cause this capacitor to be negatively charged so as to cut o tube 98 than is required to negatively charge the normally discharged capacitor 130 so that it will cut oit tube 129. For these reasons, the tube 129 will be cut oi when input pulses appear on Wire 95 at a relatively slow rate, corresponding to a very slow car speed such as one-half mile per hour.

When tube 129 is cut off, its voltage tends to rise to the level of the (B+) voltage supply. The rate of rise of this voltage is, however, limited by the rate at which capacitor 139, connecting the plate of tube 129 to ground, can charge through plate resistor 13. Therefore, if tube 129 becomes nonconductive only momentarily as a result of some spurious input pulses, the plate voltage will not rise appreciably to affect the output of tube 132. A capacitor 149, connecting the control grid of tube 132 to ground, is provided for similar reasons. If, however, tube 129 remains nonconductive for a time longer than some preselected minimum, tube 132 will become conductive and cause relay CK to pick up. Momentary interruptions in the pulsing input do not cause relay CK to drop away because capacitors 139 and 149 tend to maintain the plate and grid potentials of tubes 129 and 132 for a limited time.

Operation f Exit Relay Control Umt The beat frequency output of the preamplifier 13 is applied over wire 140 to the exit relay control unit 19 shown in FIG. 2B. This exit relay control unit 19 cornprises the clamping diode 141, cathode follower amplilier tube 142, charging diode 143, and relay control tube 144.

The beat frequency signal, having a wave form somewhat as shown at line B of FIG. 4, is applied through capacitor 146 to the control grid of tube 57. The gridcathode circuit of tube 57 includes the potentiometer 147 connected from the (B-), to ground. A preselected negative voltage level determined by the position of the tap on the potentiometer 147 is thus applied through resistor 148 to the control grid of tube 57. Resistor 148 is shunted by the clamping diode 141 which is so connected that its cathode is connected to the control grid of tube 57.

The function of the clamping diode 141 is to cause the output of the cathode follower tube 57 to vary in accordance with the peak-to-peak amplitude of the beat frequency signal appearing on wire 140 and to have this output be independent of the wave shape of this beat frequency signal as obtained from the preamplifier 13. If the clamping diode 141 were not employed and the grid cathode circuit of tube 57 were provided with only the usual operating bias voltage, the voltage at the grid of tube 57 would vary by equal amounts above and vbelow this bias level only provided that the signal appearing on wire 140 were possessed of symmetrical characteristics. The signal that appears on wire 141D may under certain conditions, however, be sufficiently distorted so that it experiences unequal positive and negative excursions about its average value. This distortion may arise in the preamplifier which is required to amplify a very Weak signal when an approaching car is at some distance from the horn and is also required to amplify extremely large signals when the car is directly over the horn 10. Because of the extreme range in amplitudes of the input signal to the preamplifier, clipping of the voltage wave form may occur with positive and negative half cycles being clipped unequally so that unequal positive and negative excursions about its Vaverage value occur.

The variation in positive excursions above the average value of `the input signal -applied to the exit relay` control unit 19V would cause the control grid of tube 57 to reach different positive peak values .of voltage for the same peak-to-peak .amplitude of beat frequency signal in accordance with the. distortion produced. It is the dropping away of the ,exit relay EX when -the beat frequency signal has reached a low amplitude that provides the indication that a car has passed out of the retarder. Thus, it might readily occur, if the clamping diode141 were 1@ not provided, that the distortion Vof the input wave form when the beat frequency signal is of a large value would result in a substantial lowering of the positive voltage to which the grid of tube 57 is driven, thereby causing the relay EX to drop away when, in fact, the car is still on the retarder.

The use of the clamping diode 141 causes the output of the cathode follower tube 57 to be dependent entirely on the peak-to-peak amplitude of the beat frequency signal and independent of the distortion that occurs. More specifically, the plate of diode 141 is connected to a negative source of voltage as already described which is provided by the potentiometer 147. As the voltage on wire 146 first rises in response to the beat frequency signal, the control grid of tube 57 has its voltage varied accordingly because the high time constant path provided for the charging and discharging of capacitor 146 through resistor 148 when diode 141 is nonconductive is sufficiently long so that this capacitor cannot receive any substantial charge. However, upon negative half cycles of input signal, the voltage on wire is driven below the voltage applied to the plate of diode 141 so that the diode 141 becomes conductive and provides a low time constant path for charging capacitor 146. Capacitor 146, therefore, becomes charged to the maximum vol*- age difference reached between the negative peak of the input signal and the voltage applied to the plate of diode 141 by potentiometer 147. Thus, regardless of the amplitude of the input signal, the control grid of tube 57 can never become more negative than the level of voltage applied to the plate of diode 141.

When the input signal rises from its negative peak value, the voltage at the cathode of diode 141 tends to rise above its clamped value so that this diode becomes immediately nonconductive. The capacitor 146 can then discharge only through the resistor 148, but as already described, this discharge path allows the capacitor 146 to discharge only very slightly between successive cycles of the beat frequency input. Consequently, the voltage at the grid of tube 57 follows the input voltage closely. On the next negative half cycle of the input beat signal, the diode 141 becomes momentarily conductive to allow the capacitor 146 to charge again to the difference in amplitude between the clamping voltage and the negative peak of the input to it, thereby restoring to capacitor 146 the amount of charge that it lost between snccessive input cycles. In this way, the negative peak of the input wave is clamped at the control grid of tube 57 at a level determined entirely by the voltage applied to the plate of diode 141 by the potentiometer 147. The control grid of tube 57 is thus driven positively from this clamped voltage level only in accordance with the peakto-peak amplitude of the beat frequency signal, without regard to its waveform.

The positive voltage pulses appearing across the cathode load resistor 150 of tube 57 when the input to the tube overcomes its normal cut-off bias and allows tube 57 to conduct are applied through resistor 145 and the charging diode 143 to the capacitor 151 and its parallel resistor 152. In this way, capacitor 151 is charged to a positive voltage whose amplitude is proportional to the peak-to-peak amplitude of the beat frequency signal.

Although the zero grid voltage of tube 144 causes it to be normally conductive, its control grid must be driven further positive by a substantial amount to cause relay EX to pick up. For a particular value of positive voltage across capacitor 151, corresponding to a preselected amplitude of the beat frequency signal, the conduction of tube 144 increases to a level that carries relay EX to be picked up,

Resistor 152 allows the charge on capacitor 151 to leak off when the beat frequency signal diminishes in amplitude and so allows the grid voltage of tube 144 to decrease to a level where the plate current of tube 57 is no longer able to hold relay EX actuated. Thus, when a car has passed over the transmitting and receiving horn l@ and the reflected signal received from such car has diminished to a level where tube 57 will no longer become conductive, the charge on capacitor 151 will be dissipated and cause a lowering of conduction of tube 144 so that relay EX will drop away. The dropping away of this relay provides the indication to the retardation selection circuits 23 that the car has passed out of the retarder.

Having described an electronic speed measuring apparatus for continually measuring the speed of cars through a railroad classification yard as one speciiic embodiment of the present invention, we desire it to be understood that this form has been selected to facilitate in the disclosure of the invention rather than to limit the number of forms it may assume; and it is to be further understood that various modiiications, adaptations, and alterations may be applied to the speciiic form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention.

What we claim is:

1. In a system for continuously measuring the speed of railway cars to provide car speed data for the automatic control of retarders in a classiiication yard, circuit means for transmitting a high frequency signal toward each approaching car and for receiving a portion of said signal being reflected from said approaching car, circuit means being responsive to both said transmitted and reflected signals and providing an output signal equal in frequency to the difference in frequency between said transmitted and reflected signals, circuit means responsive to said difference frequency and providing an output pulse for each cycle of said difference frequency with all of said pulses being of the same amplitude, a plurality or" speed indicating relays, control circuit means for each of said relays comprising a capacitor being charged by said pulses to a voltage dependent on the rate at which said pulses occur, means associated with each capacitor for causing the corresponding relay to be actuated when said capacitor is charged to a predetermined voltage level, clamping circuit means associated with each capacitor and acting on said pulses to control the portion of said amplitude of said pulses effective to charge the respective capacitor thereby causing said capacitor to become charged to its predetermined voltage level causing actuation of the associated relay for a particular respective rate of said input pulses to cause said relays to be actuated for diiferent ranges of car speeds, whereby the operated conditions of said relays provide an indication as to the speed range of said car.

2. In a system for continuously measuring the speed of moving vehicles, circuit means for transmitting a high frequency signal toward each approaching vehicle and for receiving a portion of said signal being reflected from said approaching vehicle, circuit means being responsive to both said transmitted and said reilected signals and providing an output signal equal in frequency to the difference in frequency between said transmitted and said rellected signals, circuit means including a gas discharge tube having a plate load impedance and being controlled to a conductive condition for each cycle of said beat frequency signal, means associated with said tube to cause it to be rendered non-conductive each time it is controlled to said conductive condition to thereby cause said tube to provide an output pulse across said load impedance being of constant amplitude irrespective of the amplitude of said beat frequency signal, a speed relay, and relay control means responsive to a predetermined rate of occurrence of said pulses to actuate said relay, said relay control means being etfective to maintain said relay actuated in response to pulses at any rate exceeding said predetermined rate.

3. In a system for continuously measuring the speed of railway cars to provide car speed data for the automatic control of retarders in a classification yard, circuit means for transmitting a high frequency signal toward each car and for receiving a portion of said signal being reliected from said car, circuit means being responsive to both said 2@ transmitted and reiiected signals and providing an output signal equal in frequency to the diference in frequency between said trmismitted and retlected signal, circuit means responsive to said difference frequency and providing an output pulse for each cycle of said diiference frequency with all of said pulses being of the same amplitude, a plurality of speed indicating relays, a capacitor associated with each relay, circuit means responsive to the voltage across each capacitor to control the energization of the correspond-ing relay, charging circuit means for each capacitor including a clamping rectier and a source of direct-current voltage of variable amplitude to cause a selected portion of the amplitude of each of said pulses of constant amplitude to be effective to charge the respective capacitor, each of said capacitors thereby becoming charged to the voltage level resulting in actuation of the associated relay for a diiferent rate of said pulses and a corresponding difference in car speed, whereby the operated conditions of said speed indicating relays provide information as to the range of speed of each car.

4. in a system for the automatic control of retarders in a railway car classication yard, circuit means for transmitting a high frequency signal from an antenna located along the trackway toward one end of each vehicle while it is within a retarder and for receiving a portion of said signal being reiiected from said vehicle, circuit means being responsive to both said transmitted and said reflected signals and providing an output signal equal in frequency to the difference in frequency between said transmitted and reiiected signal, exit circuit means including an electromagnetic relay being selectively energized according to the amplitude of said output signal and comprising, amplifier circuit means including an electron tube having said output signal applied to its control gridcathode circuit, blanking circuit means including rectifier means and a source of voltage of a predetermined level being associated with the grid-cathode circuit of said tube to clamp the lower limit of said grid input voltage to said fixed voltage level thereby causing said grid voltage to always vary above said fixed voltage level according to its peak-to-peak amplitude regardless of any asymmetry of said output signal, and relay control circuit means for controlling the energization of said exit relay in accordance with the positive excursion of said grid voltage of said tube, whereby said relay is caused to be in an actuated condition when a vehicle is passing over said antenna but said relay is operated to its opposite condition upon the passage of said vehicle out of said retarder.

5. Apparatus for controlling the speed of a free rolling car in a stretch of railway track extending from a hump to a desired destination in a classification track comprising,

a car retarder at an intermediate point in said stretch of track, i

said car retarder being operable selectively to any on of a plurality of braking positions and to nonbraking position,

velocity indicating means for generating a signal continuously related to the velocity of the car as it passes through the retarder,

track characteristics determining means for selecting a signal corresponding to the track characteristics from said retarder to said destination,

computing means including said track characteristic determining means and at least one parameter relating to the free rolling behavior of the car for cornputing an analog of the exit speed at which the car should leave the retarder to arrive at its destination at a desired coupling speed,

a plurality of multiple condition devices actuated jointly to one condition in response to the generation of a relatively high signal by said velocity indication means and actuated to another condition upon reduction of the speed of the car to different speeds respectively related to said analog of the exit speed,

and means for controlling said retarder to actuate it to a braking position selected by said devices to provide an extent of braking determined by the number of said devices that is in said one condition, said car retarder being actuated to a nonbraking position when said devices are all in said another condition.

6. Apparatus for controlling the speed of a free rolling car according to claim 5 wherein said velocity indicating means includes ultrahigh frequency transmitting and receiving apparatus and an antenna having a radiation pattern including the retarder for continuously indicating the speed of the car when within the retarder.

7. Apparatus for controlling the speed of a free rolling car according to claim 5 wherein the track characteristie is selected by a relay.

8. Apparatus for controlling the speed of a free rolling car according to claim 5 wherein said devices are relays controlled by said velocity indicating means.

9. Apparatus for controlling the speed of a free rolling car according to claim 8 wherein all of said relays are energized initially when a car approaches the retarder at relatively high speed and wherein said relays are dropped away at different car speeds as the speed of a car is reduced Within the retarder.

10. Apparatus for controlling the speed of a free rolling car according to clairn S wherein the degree of braking of the retarder is decreased upon the deenergization of a rst of said' plurality of relays.

References Cited in the le of this patent UNITED STATES PATENTS 1,586,989 Haines June l, 1926 1,766,539 Prescott June 24, 1930 1,791,780 Williamson Feb. 10, 1931 2,045,201 Rabourdin June 23, 1936 2,139,324 Abeloos Dec. 6, 1938 2,178,290 Sorensen Oct. 31, 1939 2,223,224 Newhouse Nov. 26, 1940 2,331,125 Logan Oct. 5, 1943 2,361,466 Fitzsimmons Oct. 3l, 1944 2,582,316 Doehler Jan. 15, 1952 2,629,865 Barker Feb. 24, 1953 2,643,369 Manley June 23, 1953 2,721,258 Freehafer Oct. 18, 1955 FOREIGN PATENTS 921,845 France Ian. 20, 1947 

5. APPARATUS FOR CONTROLLING THE SPEED OF A FREE ROLLING CAR IN A STRETCH OF RAILWAY TRACK EXTENDING FROM A HUMP TO A DESIRED DESTINATION IN A CLASSIFICATION TRACK COMPRISING, A CAR RETARDER AT AN INTERMEDIATE POINT IN SAID STRETCH OF TRACK, SAID CAR RETARDER BEING OPERABLE SELECTIVELY TO ANY ONE OF A PLURALITY OF BRAKING POSITIONS AND TO NONBRAKING POSITION, VELOCITY INDICATING MEANS FOR GENERATING A SIGNAL CONTINUOUSLY RELATED TO THE VELOCITY OF THE CAR AS IT PASSES THROUGH THE RETARDER, TRACK CHARACTERISTICS DETERMINING MEANS FOR SELECTING A SIGNAL CORRESPONDING TO THE TRACK CHARACTERISTICS FROM SAID RETARDER TO SAID DESTINATION, COMPUTING MEANS INCLUDING SAID TRACK CHARACTERISTIC DETERMINING MEANS AND AT LEAST ONE PARAMETER RELATING TO THE FREE ROLLING BEHAVIOR OF THE CAR FOR COMPUTING AN ANALOG OF THE EXIT SPEED AT WHICH THE CAR SHOULD LEAVE THE RETARDER TO ARRIVE AT ITS DESTINATION AT A DESIRED COUPLING SPEED, A PLURALITY OF MULTIPLE CONDITION DEVICES ACTUATED JOINTLY TO ONE CONDITION IN RESPONSE TO THE GENERATION OF A RELATIVELY HIGH SIGNAL BY SAID VELOCITY INDICATION MEANS AND ACTUATED TO ANOTHER CONDITION UPON REDUCTION OF THE SPEED OF THE CAR TO DIFFERENT SPEEDS RESPECTIVELY RELATED TO SAID ANALOG OF THE EXIT SPEED, AND MEANS FOR CONTROLLING SAID RETARDER TO ACTUATE IT TO A BRAKING POSITION SELECTED BY SAID DEVICES TO PROVIDE AN EXTENT OF BRAKING DETERMINED BY THE NUMBER OF SAID DEVICES THAT IS IN SAID ONE CONDITION, SAID CAR RETARDER BEING ACTUATED TO A NONBRAKING POSITION WHEN SAID DEVICES ARE ALL IN SAID ANOTHER CONDITION. 